1. Field of the Invention
The present invention relates to a process for producing a single crystal of yttrium-iron garnet or a solid solution thereof having the formula EQU R.sub.3 M.sub.5 O.sub.12
wherein R represents Y and optionally other rare earth element and M represents Fe and optionally Al or Ga.
2. Description of the Prior Arts
The single crystals of the compound having the formula EQU R.sub.3 M.sub.5 O.sub.12
have been produced by using PbO-PbF.sub.2 type flux, BaO-BaF.sub.2 type flux or Li.sub.2 MoO.sub.4 type flux etc. Most of single crystals of the compound having the formula EQU R.sub.3 M.sub.5 O.sub.12
have been commercially produced by said methods.
In the methods, the compound of R.sub.3 M.sub.5 O.sub.12 has been dissolved in the flux having low melting point and the single crystal has been formed by gradually cooling it or utilizing the temperature gradient as the principle. However, the flux has been included in the single crystal as inclusion or impurity and it has taken a long time for the single crystal growth and the distribution of Fe, Al and Ga component in the yttrium-iron garnet has not been uniform and the defect ratio has been increased and the cost for the production has been disadvantageously increased. It has been known to produce it by a traveling zone method, wherein a small amount of a solvent for dissolving the components has been used and the powdery or molded components for the product of R.sub.3 M.sub.5 O.sub.12 have been dissolved in the solvent melted by a heater (resistant heating type) and the single crystal of R.sub.3 M.sub.5 O.sub.12 has been formed on a seed crystal at a constant speed as the principle.
However, the material of the heater has been included in the single crystal as inclusion or impurity and it has taken a long time for the single crystal growth because of no stirring.